Subject: [PWE3] clarification on draft-muley-dutta-pwe3-redundancy-bit-02.txt

From: Keng Lim <[email-masked]>
Date: Wed, 23 Jan 2008 10:57:33 -0500

hi,

I am seeking some clarification on this draft.

1) in the beginning of section 5, the draft states that the preferential
forwarding bit is set to indicate Standby state, but later in draft in
section 5.3.1.e and 5.3.2.a.ii, the usage seem to have been reversed;
i.e. the latter paragraphs seem to suggest that when the preferential
bit is set, the PW is in Active state. Is there a contradiction here or
am I reading it wrong?

2) in section 5.3, The first sentence of the first paragraph states
"There are PW redundancy applications which require that PE/T-PE nodes
coordinate the switchover to a PW/MS-PW path such that both endpoints
will be forwarding over the same path at any given time."

Isn't that an implicit requirement for all PW redundancy applications
based on definition given in section 4. regarding what Active and
Standby state means? If there are PW redundancy applications where
forwarding at both endpoints can be on different paths, what would those
scenarios be?

thanks,
keng

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From: "AISSAOUI Mustapha" <[email-masked]>
Date: Fri, 25 Jan 2008 11:47:48 -0600

Keng,
thank you for reviewing this. See below for some elements of response.

Regards,
Mustapha. 

> -----Original Message-----
> From: Keng Lim [mailto:[email-masked]] 
> Sent: Wednesday, January 23, 2008 10:58 AM
> To: [email-masked]
> Subject: [PWE3] clarification on 
> draft-muley-dutta-pwe3-redundancy-bit-02.txt
> 
> hi,
> 
> 1) in the beginning of section 5, the draft states that the 
> preferential forwarding bit is set to indicate Standby state, 
> but later in draft in section 5.3.1.e and 5.3.2.a.ii, the 
> usage seem to have been reversed; i.e. the latter paragraphs 
> seem to suggest that when the preferential bit is set, the PW 
> is in Active state. Is there a contradiction here or am I 
> reading it wrong?

MA> Thank you for catching this one. Indeed sections 5.3.1.e and
5.3.2.a.ii should be corrected to state that the bit is cleared instead.
Here is a proposal for the new text. Let me know if you have any
comments:

"5.3.1.e. If while waiting for the acknowledgment, the requesting
endpoint 
      receives a status notification message from its peer with the 
      'preferential forwarding' status bit cleared in the requested PW
and set in 	all other PWs, it must treat this as an explicit
acknowledgment of the 	request and must perform the following: 

            i. Abort the timer. 

           ii. Activate the PW path.  

          iii. Send an update status notification message with the 
               'preferential forwarding' status bit clear on the newly 
               active PW and set in all other PWs in the redudancy set,
and the 		   'request switchover' bit reset in all PWs in
the redundancy set." 

"5.3.2.a.ii. ii. Send an update status notification message with the 
               'preferential forwarding' status bit clear on the newly 
               active PW and set in all other PWs in the redudancy set,
and the 		   'request switchover' bit reset in all PWs in
the redundancy set."  

> 2) in section 5.3, The first sentence of the first paragraph 
> states "There are PW redundancy applications which require 
> that PE/T-PE nodes coordinate the switchover to a PW/MS-PW 
> path such that both endpoints will be forwarding over the 
> same path at any given time."
> 
> Isn't that an implicit requirement for all PW redundancy 
> applications based on definition given in section 4. 
> regarding what Active and Standby state means? If there are 
> PW redundancy applications where forwarding at both endpoints 
> can be on different paths, what would those scenarios be?

MA> Yes, Section 4 states the requirement to forward user packets only
on a PW in Active state, which means that both ends must have found a
common PW is that state. The sentence above is adding the requirement
*to coordinate the switchover operation* in the case of the Independent
Mode. This is mainly to address situations where the two endpoints could
not find a common Active PW or when an operator wants to make a manual
switchover for maintenance.